2008 Vol.57 No.9 総説　佐野有司

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1 Reprinted from RADIOISOTOPES, Vol.57,.9 September 2008 Japan Radioisotope Association http : //

2 µ µ µ µ µ

3 µ µ µ µ µ t λ t λ t λ λ

4 λ t λ t t

5 µ µ µ µ

6 µ

8 µ µ

9 M M M M M M M M

10 σ µ σ µ µ µ

11 588 RADIOISOTOPES Vol ５７ No ９囲で一致するので海水中で成長したことを示すそして最外苑部で再び海水より高い値を示すこの結果はアユ個体が淀川で捕獲された事実と一致するこのように概ねアユの生態に沿ったストロンチウム同位体比の変動が得られたこの分析法は海と河川を回遊する他の魚類サケやウナギに応用可能であり将来は水産学に貢献するものであろう４おわりに本総説では近年東京大学海洋研究所に設置された二次元高分解能二次イオン質量分析計 NanoSIMS を用いた直径約５ µ m のスポットでの鉛とストロンチウムの同位体測定法とその応用について概説したこれらの元素は共に放射性起源の安定同位体２０６Pb ２０７Pb ８７Sr 等を含むために天然における同位体比の変動が大きくプローブ径を５ µ m まで絞っても誤差の範囲を超えた有意な変動が得られたそしてモナザイト中の鉛同位体分析では鉱物の形成年代という地質学における重要な情報が求められた一方耳石アラゴナイト中のストロンチウム同位体分析ではアユの回遊に図７ a アユ耳石の中心から分析スポットまでの距離とストロンチウム/カルシウム比の関係を示した図と b 距離とストロンチウム同位体比の図網掛けの部分は琵琶湖大阪湾淀川の文献値を示すついての生態情報を引き出すことが可能となったこのように微小領域の安定同位体分析法は今後地質学水産学に加えてさまざまな分野に応用できる可能性を秘めている文同位体比図７b を見るとストロンチウム献濃度が低いために測定誤差が大きくなっている１ Suzuki, K. and Adachi, M., Precambrian prove- ７１２５が中心から１００ µ m までの平均値は０ nance and Silurian metamorphism of the Tsubo- ±００００９と海水の値０７０９２以下の括弧内 nosawa paragneiss in the South Kitakami terrane, Northeast Japan, revealed by Th-U-total ０００１より小さいよりの値の誤差は２ σ で０ Pb chemical isochron ages of monazite, zircon 明らかに高く琵琶湖０７１１９や淀川０７１１５ and xenotime, Geochem. J., 25, と一致するしたがってこのアユは耳石が２ Montel, J. M., Foret, S., Veschambre, M., Nicollet, １００ µ m まで成長する間は琵琶湖あるいは淀 N. and Provost, A., Electron microprobe dating of monazite, Chem. Geol., 131, 川に生息していたのであろう Sr/Ca 比とは逆５０ µ m に１００ µ m を過ぎると急激に低下し１３ Hirata, T. and Nesbitt, R. W., U Pb isotope geo- で最低値に達した後で徐々に上昇する傾向にあるこれらの８７Sr/８６Sr 比は海水の値と誤差の範３２ chronology of zircon Evaluation of the laser probe-inductively coupled plasma-mass spec-

12 Geochim. Cosmochim. Acta Chem. Geol Geology J. Anal. At. Spectrom Int. J. Mass Spectr J. Geophys. Res. B89 Suppl Geochim. Cosmochim. Acta, J. Analytical Atomic Spectrometry Geochim. Cosmochim. Acta Science, Geochim. Cosmochim Acta Geophys. Res. Lett Analy. Sci Geochem. J App. Geochem

13 Earth Planet. Sci. Lett Earth Planet. Sci. Lett Trans. Amer. Geophys. Union Science Geochim. Cosmochim. Acta Chem. Geol Hydrol. Process Appl. Geochem Sci. Total Environ Geostandards Newsletter, Geochim. Cosmochim. Acta Chem. Geol Terra Nova Bull. Fish. Res. Agency Suppl Mar. Ecol. Prog. Ser The method of and isotope measurements at about 5 µmresolution was developed by using a high lateral resolution secondary ion mass spectrometer. Sincethe both elements have radiogenic nuclides such as,, and, natural variations of isotopic ratios are large. It is possible to detect a meaningful variation in a terrestrial sample, even though the experimental error is relatively large. In the case of monazite dating, a 4 primary beam

14 was used to sputter the sample and secondary positive ions were extracted for mass analysis using a Mattauch Herzog geometry. The multi collector system was modified to detect,,,, and ions simultaneously. Based on the monazite standard from North Central Madagascar, we have determined the ratios of samples. ratios were measured by a magnet scanning with a single collector mode. 44 monazite grains extracted from a sedimentary rock in Taiwan were analyzed. Observed ages were consistent with the chemical ages by EPMA. Then NanoSIMS has been used to measure ratios in natural calcium carbonate samples. Multi collector system at the same time. Magnetic field was scanning for the counter to detect, and,while the can measure,, and, respectively. Repeated analyses of a coral skeleton standard show that / ratio agrees well with the seawater signature, after the series of corrections such as dimer,, andamass bias estimated by / ratio. The method is applied to an otolith from ayu (Plecoglossus altivelis altivelis) collected from the Yodo river, Japan. The spatial variation of / ratios was consistent with amphidromous migration of the fish, namely, born in the lake and grown in the coastal sea and finally collected in a river. was adjusted to detect,,,

2007　Vol.56　No.10　総説　中田浩二

2007　Vol.56　No.10　総説　中田浩二 Reprinted from RADIOISOTOPES, Vol.56,.10 October 2007 Japan Radioisotope Association http : //www.jrias.or.jp/ Gastroenterology Gastroenterology Gastroenterology J. Smooth Muscle Res Gastroenterology

2008 Vol.57 No.9 総説 佐野有司

2008 Vol.57 No.9 総説　佐野有司